Wire tensioning device for coil winding machines



A rii 29, 1947.

WIRE TENSIONING DEVICE FOR COIL WINDING MACHINES Filed Aug. 26, 1944Patented Apr. 29, 1947 WIRE TENSIONING DEVICE FOR COIL WINDING MACHINESOtto Wirth, Zurich, Switzerland, assignor to Micafil Ltd, Zurich,Switzerland Application August 26, 1944, Serial No. 551,360 InSwitzerland June 18, 1943 Claims. (Cl. 242156) When manufacturing wirecoils which are mechanically rotated, certain difficulties are stillencountered in connection with the unwinding of the wire from a separatesupply drum. Thus for instance during acceleration, the wire becomesstretched or even breaks, due to overstressing, and the quality of thecoil therefore depends on the perception and skill of the winder. Thewire tension should, however, not depend on this but should be keptconstant automatically.

It is not sufiicient to control the braking power acting on the supplydrum by means of the Wire tension itself. Up to the present this hasgenerally been done by passing the wire over a pulley arranged at theend of a lever the movement of which lifts the brake of the supply drumby a variable amount. The movements of the lever thus act directly onthe brake and are much too large to ensure an accurate regulation of thepower; with this arrangement variations in braking power amounting toseveral tim'sthaprescribed value have to be taken into account. '7

Furthermore the wire tension is produced spring whose force varies withthe movements of the wire guide lever. If on the other hand the tensionin the wire were produced by a weight, forces would have to be overcomewhich could easily cause the wire to be too highly stressed. The spring,and the power depending on the spring tension, cannot therefore bedispensed with. I

The aforementioned drawbacks are overcome according to the presentinvention by locating between the wire guide lever and the spring anintermediate element with a constantly varying transmission ratiodepending on the position of the wire guide lever, whereby this elementcauses the wire tension to remain constant independently ofi thetravelgithe free end of the spring.

A constructional example of the invention is illustrateddiagrammatically in Fig. 1 (elevation) and in Fig. 2 plan) of theaccompanying draw- The supply drum a is fixed by means of clamping conesc, to a mandrel b which is supported between pivot bearings d. The brakedisc 6, having a brake band 1 cooperating therewith, is also fixed tothe mandrel b. A brake lever g, pivoted at a, has unequal arms. Theshorter arm is connected at f to the brake band I and the longer arm isoperatively connected by a, link h to a lever i, the link being pivotedto lever g and lever i by pins as and y, respectively. The lever i isprovided with a guiding cam i and is supported on the shaft of the longlever It. At the outer free end of lever in a.roller m is located overwhich the wire 11. slides, and passes to the coil which is to be wound,as indicated by the arrow in Fig. 1. The tension spring 0 presses themovable roller 1) carried by a link if having a fixed pivot 0 againstthe cam portion i of lever i which has such a shape that the leveragevaries inversely proportionally to the applied spring force, so that thetorque exerted by the spring on the lever system i, 7', k and thus alsothe tension on the wire n remains constant. At the same time as lever itdrops, brake band f is released. When arm is is again returned .to itsnormal position by spring 0, the brake band I is again applied moretightly.

The spring tension can be adjusted by means of the set screw q. Thisscrew has a pointer 1' connected to it which moves along a scale s; thislatter can be calibrated to indicate the diameter of wire which willjust not be stretched at that position of the pointer. a y

The ratio of the movement of the brake band 1 to that of the wire guideroller m should be at least 1:50 so that the braking power varies withthe required accuracy. Brake band 1 preferably consists of a woven beltof linen, cotton or silk and it is an advantage to provide the brakingsurface of the brake drum c with fine grooves; by this means it ispossible to obtain smooth braking suitable for fine winding wires.

In operation, as the tension on the wire n increases, due to windingconditions, the long lever It moves counter-clockwise and carries withit cam lever 2'. This movement causes the link 71. to rock the lever gcounterclockwise and thus releases some of the tension on the brake bandi. This permits the drum a to rotate more freely and the tension on thewire n is correspondingly reduced. At the same time the roller p ismoved in a clockwise direction about the pivot 12 and the tension of thespring 0 is correspondingly increased. However, the shape of the camsurface 2" is such that the torque resulting from this increased springtension is not transmitted to the long lever is but, instead remainssubstantially constant. The reverse of the foregoing sequence offunctions takes place when the tension of the wire n is restored tonormal.

Instead of a hand brake it is of course possible to employ any othersort of brake, it only being necessary to arrange the brake to suit themeans for regulating the braking power.

I claim:

1. In a device for maintaining an allowable wire tension at the supplydrum of a. coil winding machine where the drum has a brake acting on itin dependence on the tension in the wire and the coil is mechanicallydriven, in combination, a wire guide lever, a roller carried by saidlever over which the wire passes, a counter spring for biasing saidlever to tension the wire, the tension in said spring being variablewith any momentary variation in wire tension, and means maintaining thebiasing effect of said spring on said lever substantially constantregardless of any fluctuation in spring tension comprising anintermediate element with a variable transmission ratio depending on itsposition operatively interconnecting said lever and said spring, saidtransmission ratio varying inversely with the spring tension.

2. Device as in claim 1, characterized by the feature that theintermediate element is a lever whose effective length with respect tothe force applied by the spring varies with its position.

3. Device as in claim 1, characterized by the feature that theintermediate element is a lever having a cam surface arranged andadapted to vary the effective length of the lever with respect to theforce applied by the spring as the lever position varies.

4. Device as in claim 1, characterized by the feature that the brake onthe supply drum is 01!- eratively connected to and is controlled by thesam lever system as the counter spring.

5. Device as in claim 1, characterized by the feature that the brake onthe supply drum is operatively connected to and is controlled by thesame lever system as the counter spring, and by the feature that theratio of the movement of the movable part of the brake to that of thewire guide roller is at least 1:50.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,677,167 Borgeson July 17, 19282,008,873 Nydegger July 23, 1935 2,219,196 Nystrom et a1. Oct. 22, 19402,331,371 Bridges Oct. 12, 1943 2,363,677 Krik Nov. 28, 1944 724,975Wardwell Apr. 7, 1903

